The present invention relates in general to a storage subsystem and its control method, and relates in particular to a storage subsystem adopting a redundant path configuration and which includes a connection path formed from a plurality of switch devices, and a control method of such a connection path.
A storage subsystem is an apparatus adapted for providing a data storage service to a host computer. A storage subsystem is typically equipped with a plurality of hard disk drives for storing data and a disk controller for controlling the plurality of hard disk drives. A disk controller includes a processor for controlling the overall storage subsystem, a frontend interface for connecting to a host computer, and a backend interface for connecting to a plurality of hard disk drives. Typically, a cache memory for caching user data is arranged between the interfaces of the host computer and the plurality of hard disk drives. The plurality of hard disk drives is arranged in array via switch circuits arranged in multiple stages.
Since a storage subsystem is generally used in mission critical business activities, it is demanded of high reliability and high availability. Thus, in view of fault tolerance, components in the storage subsystem are typically configured redundantly. For example, the path for accessing the hard disk drive is made redundant in the backend interface so that, even if one of the paths is subject to a failure, the other path can be used to operate the system without interruption. Moreover, if a failure occurs in the storage subsystem, the component subject to such failure is identified immediately and failure recovery is performed.
Japanese Patent Laid-Open Publication No. 2007-141185 discloses a storage controller that monitors a plurality of ports of a switch circuit connected to a disk drive, identifies the fault site with a failure recovery control unit provided to the controller upon detecting an error in any one of the ports, and thereby performs failure recovery processing.